Methods of spectrally sensitizing silver halides with dyes are a known technique, and as practicable sensitizing dyes, methine type dyes having adsorbability such as cyanine, merocyanine, composite cyanines and composite merocyanines are widely used. These dyes are used to enlarge the wavelength range of color sensitization and are in some cases supersensitized. Generally it is known that these spectral sensitizinig dyes are adsorbed on silver halide grain surfaces to take part in sensitization. Thererfore, the larger the adsorption effective surface area per grain of a silver halide, the larger the light absorption quantity of the adsorbed sensitizing dye, which increases the spectrally sensitized sensitivity. In this respect, tabular silver halide grains having a large surface area/volume ratio are advantageous to give a high spectral sensitivity in comparison to cubic, octahedral, or sperical grains, and therefore the tabular silver halide grains are considered advantageous to provide an emulsion that is highly sensitized with a dye. Particularly, since silver bromoiodide tabular emulsions are preferable from a practical viewpoint in that the intrinsic sensitivity is high, various dye sensitizations and supersensitizations thereof have been studied. That is described in detail, e.g., in Research Disclosure, RD No.22534 (Jan. 1983) and Japanese patent application (OPI) Nos. 113926/83 and 113927/83 (the term "OPI" as used herein refers to a "published unexamined Japanese Patent Application).
On the other hand, there is a limit on the quantity of a spectral sensitizing dye to be adsorbed onto emulsion grain surfaces, and it is well known that when saturated adsorption or adsorption near to saturation is established, remarkable desensitization (intrinsic desensitization) often takes place (see, for example, Photog. Sci. Eng. by W. C. Lewis, et al., Vol. 13, page 54, 1969, and U.S. Pat. No. 3,979,213) and that the optimum amount of a sensitizing dye to be added is that amount generally corresponding to about 25 to 100% of the surface covering rate of the grains (see Theory of the Photographic Process, by K. Mees, 1942 Macmillan, page 1067). This also applies to tabular emulsions (see Japanese patent application (OPI) No. 113926/84), and the situation is such that the rate of use of incident light is still quite low.
Further, since grains of tabular emulsions have large specific surface areas, an increase in sensitivity by color sensitization, that is, the ratio of the minus blue sensitivity to the blue sensitivity (intrinsic sensitivity), is high, so that although tabular emulsions are advantageous when a green sensitive layer or a red sensitive layer is to be highly sensitized, the sensitivity of a blue sensitive layer, in comparison to that of the green sensitive layer or the red sensitive layer, is relatively low, which results in color imbalance. This is described in Japanese patent application (OPI) Nos. 113927/83, 113930/83, and 113934/83 wherein it is pointed out that since the blue sensitivity is low, it is not required to provide yellow filters for the green sensitive emulsion layer and the red sensitive emulsion layer, both layers being applied on a color sensitive material. The same problem occurs in cases using panchromatic black and white photosensitive materials whose tabular emulsion is sensitized in the range of from blue to red. That is, in these cases, it is required to add a blue sensitive dye to improve blue sensitivity, whereas, due to a limit to the dye adsorption amount, this inevitably reduce the sensitizing dye for minus blue sensitization, and, as a result it becomes difficult to retain the minus blue sensitivity at a high enough value.